I am getting strange shadows when using hair cards and cycles
I've lined up several transparent planes here as shown.

You can see that in rendered view we get some shadows on the ground even though these planes shouldn't affect anything.

This is because the ray cast from the camera hits the Transparency bounce maximum (which is low-ish by default), and reports back that the ray was lost, giving the color black.
Raising the value under Render properties -&gt; Light paths -&gt; Transparency should fix this.